1、request.getRequestURL()
返回的是完整的url，包括Http协议，端口号，servlet名字和映射路径，但它不包含请求参数。
2、request.getRequestURI()
得到的是request URL的部分值，并且web容器没有decode过的
3、request.getContextPath()
返回 the context of the request.
4、request.getServletPath()
返回调用servlet的部分url.
5、request.getQueryString()
返回url路径后面的查询字符串
示例：
当前url：http://localhost:8080/CarsiLogCenter_new/idpstat.jsp?action=idp.sptopn
request.getRequestURL() http://localhost:8080/CarsiLogCenter_new/idpstat.jsp
request.getRequestURI() /CarsiLogCenter_new/idpstat.jsp
request.getContextPath()/CarsiLogCenter_new
request.getServletPath() /idpstat.jsp
request.getQueryString()action=idp.sptopn
当前url：http://localhost:8080/Enterprise/EntUserServlet?action_flag=jumpReg
httpRequest.getRequestURL()+"?" + httpRequest.getQueryString() http://localhost:8080/Enterprise/EntUserServlet?action_flag=jumpReg
httpRequest.getRequestURI()+"?" + httpRequest.getQueryString() /Enterprise/EntUserServlet?action_flag=jumpReg
httpRequest.getServletPath()+"?" + httpRequest.getQueryString() /EntUserServlet?action_flag=jumpReg
来自：http://blog.csdn.net/gris0509/article/details/6340987